Preparation And Properties Of Acrylate Pressure Sensitive Adhesive Grafted With Degradable Copolyester

Acrylic resin pressure-sensitive adhesive(PSA)with high biomass contents were prepared by grafting biodegradable copolyester macromonomers(MM)to acrylic resin main chains.Aggregation processes of acrylic copolymers,including the phase separation assembly,were controlled through regulation of MM chain structure,length and graft density.Generated comb-structures possess broadened glass transition regions,physical crosslinking and greater chain entanglement resulting in enhanced tack force(tack),peel strength(peel),and shear resistance(shear).Development of this novel material involved efforts on a series of issues.An initial objective was the identification of viable organic catalyst to replace Sn(Oct)2 in MM reactions.The influence of a variety of different catalysis and feed strategies on the structure of L-lactide/?-caprolacton(L-LA/?-CL)copolyester MMs were examined.The organic catalyst rac-BNPH was found to sufficiently promote the copolymerization of L-LA and ?-CL and also limit transesterification reactions,which are quite prevalent with Sn(Oct)2.It was found that ?-CL is the active monomer in the rac-BNPH catalyzed reactions,and by controlling the addition of ?-CL,a well-distributed copolyester MM structure can be obtained.The influence of MM chain length and structure were investigated by copolymerizing commonly utilized acrylic monomers to produce acrylic resin grafted with polyesters.Fixing the feeding molar ratio of L-LA and s-CL at 5/4,a range of different length MM were generated using the Sn(Oct)2 catalyst system.The glass transition temperature(Tg)of MMs increased with the increase of chain length,while the Tg of block MMs with the same feeding molar ratio did not change with chain length.Also crystallization of PCL and PLLA components were found for long chain block MMs.The connection between polymer microstructure and mechanical properties was examined through the transitional free radical copolymerization of a series of acrylic resins grafted with different chain length polyester MM chains.Again,feed molar ratio of L-LA and ?-CL was fixed at 5/4.The MM chains were found to all possessed a random structure.The resins with the shortest graft chains,PL10C4 and PL20C8,were homogenous and demonstrated high tackiness and rheological behavior consistent with the Rouse model.For the polymers possessing the longer graft chains(MMs),PL50C20 and PL100C40,phase separation occurred.The low frequency rheological behavior of these polymers behaved as a lamellar phase separation with the phase separation between columnar and cubic.These polymers also showed improved peel and shear performance.In addition to varying the composition of the MM,a series of acrylic resin grafted with different MM contents were characterized.The polymer possessing lowest MM content,PB-C4L10-33%showed decent mechanical properties.With increasing of polyester side chains,two glass transitions appeared and indications of PLLA crystallization were found in the DSC thermograms.This was accompanied by a decline in adhesive performance.When the amount of B-C4L10 was increased to 50 wt.%,PB-C4L10-50%,phase separation was apparent and the copolymer demonstrated rheological behavior consistent with a lamellar phase separation.The tack of these polymers decreased slightly,but their peel strength and creep resistance improved.Besides producing the graft copolymer via solution polymerization,it was shown that similar structures are obtained using mini-emulsion polymerization.This approach was used to produced polymers containing 33wt.%L10C4 MM.It was determined that the mini-emulsion system could be stabilized with 3wt.%of the emulsifier using a combinations of OS-15 and AES at a fixed weight ratio at 1:2.In summary,this project resulted in a number novel findings.It was shown that strategic feed strategies on rac-BNPH catalyzed ring-opening copolymerization of L-LA and ?-CL can be used to limit transesterification reactions and tailor copolyester MM structure.Adjustments to the structure and chain length of the graft copolymers can be used to effectively control the aggregation structure of the acrylate copolymer,especially the microphase separation structure.By balancing the effect of entanglement,phase transition behavior and physical crosslinking,good mechanical properties we obtained.Furthermore,the proper choice of an emulsifier system provided for the generation of a stable mini-emulsion acrylate PSA with a high biomass content.