NOTE：Pinova^®, Piccolyte^®, Kraton^®, DRT^®, and Dercolyte™ are registered trademarks or trademarks of their respective owners. All product names, logos, and brands mentioned in this document are the property of their respective trademark holders. Use of these names, logos, or brands is for identification purposes only and does not imply any affiliation with or endorsement by the trademark holders.

Terpene resins prepared from alpha-pinene

The Piccolyte^® A-series resins, such as A115 and A125, originally produced by Pinova^® (now DRT^® under the Dercolyte™ A115, A125 names), are widely used tackifying resins for hot melt adhesives and solvent-based glues. These resins are highly favoured by product developers due to their ability to enhance initial tack, peel strength, and heat resistance.

The Piccolyte^® A-series terpene resins are prepared from high-purity α-pinene through a complex modification process, and are characterised by their low odour and light colour (Gardner colour ≤ 2). Owing to the bridged-ring structure of the α-pinene monomer, the modified polymer structure becomes compact after polymerisation, making it more resistant to oxidation and chain scission. This structural stability makes it well-suited for demanding applications involving prolonged thermal ageing and outdoor UV exposure.

On the other hand, the backbone structure of α-pinene, once modified, contains non-polar functional groups, resulting in very low molecular polarity. Terpene resins derived from α-pinene are classified as non-polar polymers and exhibit excellent compatibility with non-polar or weakly polar elastomers, such as the butadiene block in SBS, the isoprene block in SIS, and natural rubber.

Elastomer Type	Compatibility with terpene resin prepared from α-pinene
SBS / SIS	Terpene resins derived from α-pinene exhibit good polarity matching with the mid-block segments (butadiene, isoprene), while the polystyrene end blocks are typically immiscible. However, the blend tends to form a co-continuous “soft phase–hard phase” structure.
SEBS	SEBS is the hydrogenated form of SBS and exhibits even lower polarity. However, α-pinene-based terpene resins still maintain good compatibility with its mid-block segments, which resemble polyethylene chains.
Natural Rubber (NR)	α-Pinene-based terpene resins exhibit a synergistic effect with the conjugated diene structures and low-polarity segments in natural rubber (NR), enhancing viscoelasticity without disrupting the integrity of the adhesive matrix.
EVA / APAO / POE	If the VA content is low (<20%), the polarity remains low, allowing the formation of a physical blend phase with α-pinene-based terpene resins.
TPU / PVB / NBR	Excessively high polarity can lead to phase separation, and direct blending is therefore not recommended.

In general, conventional C5 petroleum resins have a glass transition temperature (Tg) typically below +25 °C, while standard rosin-modified resins exhibit a Tg range of approximately +30 to 55 °C. A higher Tg contributes to improved adhesive rigidity and heat-resistant shear performance, which is particularly advantageous in hot melt pressure-sensitive adhesives (HMPSAs) or other adhesive systems based on SBS elastomers.

Terpene resins prepared from α-pinene not only provide initial tack but also contribute structurally to the adhesive matrix by forming part of the “supporting phase”. Thanks to their rigid molecular structure and relatively high Tg, these resins resist cold flow and migration in the molten state, thereby offering excellent structural support.

Moreover, their molecular structure shows a degree of segmental compatibility with the polystyrene (PS) end blocks of SBS. This allows closer interaction and aggregation at the microscopic level, enhancing interfacial adhesion. Such intermolecular interactions help improve the system’s shear strength and resistance to deformation, making these resins especially suitable for applications requiring high structural integrity and thermal stability.

The α-pinene-based terpene resins mentioned above possess several advantages, including light colour, low odour, high Tg value, high biobased content, and excellent compatibility with elastomers. As a result, these terpene resins are now widely used in demanding formulations such as medical pressure-sensitive adhesives and electronic pressure-sensitive adhesives.

Terpene resins prepared from α-pinene exhibit a range of advantageous performance properties; however, they also present certain limitations in terms of chemical reactivity. Firstly, due to the saturated bridged-ring structure of α-pinene, these resins lack active functional groups such as hydroxyl or carbon–carbon double bonds, which are essential sites for participation in photoinitiated reactions. UV curing typically relies on radical polymerisation, cationic polymerisation, or block polymerisation. Without functional modification, terpene resins generally do not take part in the polymerisation or crosslinking processes during UV curing, instead behaving as inert or non-reactive fillers.

Furthermore, the modified terpene resin molecules tend to have rigid chain structures, which limit the segmental mobility and diffusivity required in the early stages of photopolymerisation. This lack of mobility can hinder a fast and uniform photo-crosslinking process.

For applications involving UV inks, 3D printing materials, or UV-curable adhesive systems, the mainstream approach to enabling the use of terpene resins is to further modify them through acrylation. By reacting with unsaturated carboxylic acids such as acrylic acid, methacrylic acid, or their derivatives (e.g. GMA, HEMA, MAA, AA), acrylate or methacrylate groups capable of free-radical polymerisation can be introduced onto the backbone or side chains of the terpene resin via esterification or addition reactions.

These functional groups can rapidly polymerise and crosslink under UV irradiation in the presence of a photoinitiator, forming a cured film. The modified terpene resins feature a defined molecular weight, low volatility, and a high density of reactive sites, offering a good balance between crosslinking efficiency and film-forming performance in UV ink, 3D printing resin, and related systems.

In addition to acrylation, another mainstream approach involves copolymerisation modification to introduce UV-reactive functional groups. This includes both graft copolymerisation and block copolymerisation methods. By incorporating monomers or segments containing functional groups required for UV curing—such as acrylates, methacrylates, or epoxides—into the backbone or side chains of terpene resins, their ability to participate in photo-crosslinking reactions can be effectively enabled.

This strategy typically relies on a free-radical initiation mechanism, whereby functional monomers undergo graft polymerisation in the presence of terpene-based resins, resulting in functional materials with UV-responsive properties. Such copolymer modification techniques, based on naturally derived monoterpene structures, are increasingly becoming a research focus in the development of sustainable UV-curable materials.

Graft Polymerisation Strategy
Graft Copolymerisation	This involves introducing UV-reactive functional groups onto the backbone or side chains of terpene resins using monomers such as maleic anhydride (MAH), acrylic acid (AA), or glycidyl methacrylate (GMA).
Block Copolymerisation	This approach constructs reactive polymer blocks—such as PEG‑b‑TPGDA or PU‑b‑HEMA—through polymerisation reactions to form functional block copolymers with terpene structures. These modifications are typically achieved using radical initiators, which induce the graft polymerisation of functional monomers in the presence of terpene resins. This strategy represents a key area of research for extending the application of natural resins into the UV-curable materials field.

In addition, α-pinene-based terpene resins present an objective cost disadvantage. As α-pinene is derived from gum turpentine, its availability is subject to fluctuations in global supply, market conditions, and environmental regulations. Consequently, formulations using pure pinene-based terpene resins generally incur higher costs compared to conventional petroleum-based C5/C9 resin systems. Furthermore, due to the more demanding polymerisation processes required, these formulations are also typically more expensive than those based on standard rosin-modified resins.

In response to this situation, the market has widely adopted a “cost reduction and performance enhancement” strategy by blending terpene resins with petroleum-based resins. For example, our AP series of terpene-phenolic resins offer performance fully comparable to competing terpene resin products. By flexibly adjusting the blending ratio between terpene and petroleum-based resins, we are able to effectively control formulation costs and achieve cost-reduction objectives.

Compatibility of elastomers

The Kraton™ SBS D1** series is a block copolymer composed of styrene and butadiene, typically exhibiting a linear (triblock) or star-shaped (multiblock) structure. It belongs to one of the most widely used categories of styrenic thermoplastic elastomers (TPS). Combining thermoplastic processability with rubber-like elasticity, it serves as a key component in pressure-sensitive adhesives, hot melt adhesives, and modified materials.

Due to its high strength, broad hardness range, and low viscosity, it is widely applied in areas such as pressure-sensitive adhesives, modified bitumen, modifiers, hot melt adhesives, clear rigid packaging, and soft plastics. The Kraton™ SBS D series consists of polystyrene (PS) and polybutadiene (PB) blocks, forming a typical ABA block copolymer structure. The butadiene block contains a certain proportion of unsaturated double bonds, which makes it somewhat susceptible to thermal-oxidative ageing. However, when stabilised with appropriate antioxidant systems (such as hindered phenols or aromatic amines), its thermal ageing resistance is sufficient to meet the demands of most applications.

The styrene block acts as the hard segment, forming physical crosslinking points within the material that enhance overall mechanical strength and recovery from deformation. This synergistic soft–hard block structure of SBS makes it well-suited for use in tapes, sealants, and other applications requiring long-term elasticity and repeated stretchability.

The molecular weight and glass transition temperature (Tg) of tackifying resins are key factors influencing their initial tack performance. Low molecular weight and low Tg contribute to improved surface wetting of the resin, thereby enhancing initial tack. On the other hand, the presence of SBS elastomers can indirectly affect initial tack by restricting the resin’s ability to migrate and rearrange at the surface through their physical crosslinking structure. This, in turn, regulates the immediate contact behaviour between the adhesive surface and the substrate.

Elastomers themselves do not possess inherent tack; within adhesive systems, they primarily serve as the structural “elastic phase” and must rely on synergy with tackifying resins to achieve actual adhesion. Theoretically, the higher the proportion of SBS, the greater the system’s structural support and resilience. However, this can also inhibit the migration and wetting behaviour of tackifying resins, potentially leading to reduced initial tack performance.

Taking the Kraton™ SBS D1** series as an example, this series features an ABA-type block copolymer structure, composed of rigid polystyrene (PS) end blocks and a flexible polybutadiene (PB) midblock. The PB segment imparts elasticity to the material and also contributes, to some extent, to the development of adhesion properties. When SBS is used in combination with tackifying resins, the latter microscopically mix with the PB block, thereby adjusting the overall flowability and surface wetting of the adhesive matrix, which in turn influences the initial tack performance.

Building on this, the selection of an appropriate low molecular weight tackifying resin can create flowable microdomains within the SBS elastic network. These microdomains tend to migrate towards the adhesive surface, facilitating rapid wetting of the substrate and the formation of instantaneous adhesion points, thereby enhancing overall initial tack performance.

So why do some resins perform poorly in terms of initial tack when combined with SBS? This is generally attributed to two main factors:

1. Excessive proportion of the elastic phase: When the SBS content is too high, the adhesive layer exhibits strong elasticity and shape recovery. During the pressing process, part of the applied energy is absorbed by the elastic network, resulting in insufficient wetting of the adhesive surface on the substrate, which weakens the instantaneous bonding ability.
2. Poor wetting performance of the tackifying resin: This is particularly evident when using rigid resins such as high-Tg, high molecular weight C9 petroleum resins. Due to their limited chain mobility and slow wetting kinetics, these resins are less able to migrate quickly to the adhesive surface. When combined with the structural constraints of the SBS network, it becomes even more difficult for them to establish sufficient surface contact, further reducing initial tack performance.

However, not all tackifying resins lead to reduced initial tack in SBS-based adhesive systems. In contrast, terpene resins—typically characterised by relatively low molecular weight and comparatively high Tg—tend to offer a better balance between wetting ability and structural support. Their strong surface migration capability facilitates rapid wetting of the substrate, while the higher Tg provides a certain level of initial modulus without compromising the structural integrity of the adhesive.

Moreover, terpene resins are prepared from renewable biobased resources. When blended with petroleum-based resins such as C5 and C9, they can partially replace high-cost pure terpene resin formulations to control costs, while also significantly improving the initial tack and flow behaviour of traditional systems. As a result, terpene resins are increasingly emerging as a next-generation tackifying solution that balances performance optimisation with environmental sustainability.

More terpene resins based on terpene monomers

In addition to α-pinene, terpene monomers such as β-pinene, dipentene, limonene, camphene, and δ-carene are also widely used in the synthesis of terpene resins. These naturally occurring terpene monomers are by-products from the distillation of gum turpentine, making them readily accessible within an integrated supply chain. Their distinct chemical structures offer diverse polymerisation potential.

“Terpenes” are a class of natural hydrocarbon compounds composed of isoprene (C₅H₈) units. Their molecular structures typically contain one or more carbon–carbon double bonds (C=C), which may be located at terminal positions, within ring structures, or present in conjugated forms. Terpene monomers are generally characterised by low molecular weight, high volatility, and high chemical reactivity, making them well-suited as starting materials for cationic, radical, or condensation polymerisation processes.

From a polymer chemistry perspective, resins are essentially high-molecular-weight polymers formed through the polymerisation of monomers. Due to the unsaturated bonds in their structures, terpene monomers offer reactive sites for various polymerisation mechanisms, providing the potential to construct a wide range of functional polymer architectures. As such, they represent a rich source of precursors for the development of bio-based functional materials.

Property Table of Resins Prepared from Terpene Monomers
Terpene monomers	Polymerisation Method	Resin Characteristics	Typical Applications
α-Pinene	Cationic Polymerisation	High rigidity, high Tg, low odour, good colour	PSA, medical adhesives, label adhesives
β-Pinene	Cationic Polymerisation	Good flexibility, excellent wetting, medium Tg	Packaging hot melt adhesives, fast-setting adhesives
Dipentene	Radical Polymerisation , Condensation Reaction	Soft chain segments, suitable for low-temperature hot melt adhesives	Soft chain segments, suitable for low-temperature hot melt adhesives
Limonene	Radical Polymerisation	High volatility, aromatic odour, suitable for eco-friendly coatings	Eco-friendly inks, adhesives
Camphene	Radical Polymerisation,Esterification	Rigid structure, enhanced support and thermal stability	Structural adhesives, high heat-resistant hot melt adhesives
δ-Carene	Radical Polymerisation, Diels–Alder Addition	Modifiable for epoxy systems, excellent heat resistance	Epoxy adhesive curing aids, modifiers

Terpene resins prepared from beta-pinene

Taking β-pinene as an example, its terminal double bond typically gives it higher reactivity and polymerisation rate than α-pinene in cationic polymerisation. However, during the polymerisation process, β-pinene is prone to isomerisation and rearrangement, resulting in polymer backbones containing cyclohexene structures. In addition, chain transfer reactions are relatively active, which leads to polymers with a broad molecular weight distribution.

Nonetheless, resins polymerised from β-pinene still maintain a light colour, good colour stability, and excellent adhesion properties. They are commonly used as tackifiers for natural rubber and polyisoprene, and are also suitable for applications such as solvent-based pressure-sensitive adhesive tapes, label production, and end-sealants for metal cans.

Terpene resins prepared from dipentene and limonene

Dipentene, also known as DL-(racemic) limonene, is a by-product of the turpentine distillation process. Its double bond structure enables it to undergo radical or cationic polymerisation, giving it polymerisation potential. Dipentene primarily polymerises through its terminal methylene group. Like β-pinene, the presence of an exocyclic or terminal methylene makes it more readily polymerisable compared to α-pinene.

Terpene resins derived from dipentene exhibit good thermal stability and oxidative resistance, making them particularly well-suited as tackifiers for SBR and SBS elastomers.

Dipentene is a racemic mixture of (R)-limonene and (S)-limonene. Upon purification, dipentene can yield limonene. The key distinction between dipentene-derived limonene and that sourced from citrus fruits in North America lies in their stereochemistry: citrus-derived limonene primarily consists of (R)-limonene. As a result, in the North American market, terpene resins produced from limonene generally refer to those made using (R)-limonene as the raw material.

However, limonene has relatively low intrinsic reactivity. This is because its internal double bond is located within a six-membered ring, where ring strain and greater steric hindrance hinder the formation of transition states, thereby reducing the reactivity of the double bond. In radical polymerisation in particular, the presence of allylic hydrogen in the limonene molecule makes it susceptible to detrimental chain transfer reactions.

Industrially, to overcome the low inherent reactivity of limonene and the instability of its polymerisation systems, various strategies are employed in the production of limonene-based terpene resins. A common approach is copolymer modification—for example, copolymerising limonene with monomers such as styrene to adjust reactivity and achieve resins with specific properties.

In addition, using specialised cationic polymerisation catalyst systems, such as a combination of aluminium trichloride and trialkylchlorosilanes, and conducting the reaction at low temperatures in suitable solvents, can help improve polymerisation efficiency and control molecular weight.

Limonene can also be used to synthesise resins through reactions with other compounds—such as phenolic compounds—to produce terpene–phenolic resins, thereby altering the reaction pathway and circumventing the limitations of limonene’s direct polymerisation. These methods enable limonene to be effectively utilised in the industrial production of terpene resins with a variety of performance profiles.

Terpene resins prepared from camphene

Like α-pinene and β-pinene, camphene also has a bicyclic structure. However, unlike the others, camphene’s core framework is a bicyclo[2.2.1]heptane structure, consisting of two fused five-membered rings—commonly referred to as a norbornane skeleton. The rings are connected via bridgehead carbon atoms, which gives this bridged-ring system high rigidity but also limits the rotational and conformational flexibility of the rings.

Compared with monocyclic structures—such as the six-membered ring in limonene—bicyclic frameworks are inherently more rigid and less prone to significant conformational changes. Camphene’s physical property of forming colourless crystalline solids at room temperature further reflects its relatively strong intermolecular forces and the stability of its molecular structure.

In the production of terpene resins, camphene is primarily utilised industrially through the following approaches: one method involves esterification of camphene with low-molecular-weight carboxylic acids in the presence of an acid catalyst to form terpene esters. These esters can be used directly as tackifying resins or as components in resin formulations. Another approach is to use camphene as a comonomer, copolymerising it with other terpene or non-terpene monomers to obtain resin materials with tailored properties.

However, compared to α-pinene and β-pinene, camphene is less commonly used on a large industrial scale for the direct synthesis of polyterpene resins. Instead, it is more often employed in the preparation of modified resins or as a specialty component to impart specific properties—such as increasing the Tg of the resin or enhancing its performance in certain applications.

Terpene resins prepared from delta-carene

δ-Carene is a structurally unique monoterpene, featuring a bicyclic system composed of a six-membered ring fused with a cyclopropane unit. In addition, it contains a carbon–carbon double bond located within the six-membered ring. This distinctive structure imparts δ-carene with both the high ring strain of cyclopropane and the reactivity of an alkene, resulting in unusual chemical properties.

As such, terpene resins prepared from δ-carene can be synthesised via Diels–Alder addition reactions with dienophiles such as maleic anhydride. The resulting polycyclic compounds can serve as curing agents in epoxy resin systems, playing a key role in resin formulation. δ-Carene can also act as a comonomer in copolymerisation with other monomers, including both terpene and non-terpene types, to modify the final resin properties—for example, to enhance specific mechanical or adhesive characteristics.

Summary

In summary, various terpene monomers, owing to their common structural features—particularly the presence of reactive carbon–carbon double bonds or condensable functional groups—can serve not only as fundamental building blocks in polymerisation reactions (such as cationic or radical polymerisation) to construct a wide range of polymer architectures, but also undergo condensation reactions with phenols, organic acids, or anhydrides to produce functional resins with differentiated physical properties.

These terpene resins, prepared from natural and renewable resources, offer excellent adhesion, thermal stability, and structural tunability. As such, they have been widely applied across industries including adhesives, coatings, inks, and composite materials, and are gradually replacing certain petroleum-based resin materials.

According to market research data, the global terpene resin market is projected to reach USD 1.13 billion by 2024, with a compound annual growth rate (CAGR) of approximately 7.4% to 7.9%. This growth trend reflects the industry’s strong demand for materials that combine high performance with environmental sustainability, further validating the important role of terpene resins as a high-potential bio-based material in future formulation design and green manufacturing.