Novel Functional Block Copolymer Combining Enzymatic Polymerization And ATRP And Its Self-Assembly Behavior Study

Enzymatic Polymerization (EP) and Atom Transfer Radical Polymerization (ATRP) have attracted considerable attentions due to their respective unique properties. However, chemoenzymatic synthesis based on functional materials in recent years. This strategy has motivated more researchers to study chemoenzyme-catalyzed routes to obtain the novel polymeric materials.The aim of this paper is to investigate and study the chemoenzymatic synthesis of functional multiblock copolymer by combining EP [including enzymatic Ring-Opening Polymerization (eROP) and enzymatic Self Condensation Polymerization (eSCP)]. Firstly, two strategies, i.e. Bifunctional initiator method and End-group Modification method, were used to carry out the integration of two fundamentally different synthetic techniques, eROP and ATRP. Functional multiblock copolymers with different structures were obtained, at the same time, the structures and properties of the resulting copolymer were investigated in detail.Subsequently, our groups also studied the eSCP involved chemoenzymatic preparation. In addition, self-assembly behavior of copolymers in aqueous media was also studied by the numbers.In the first section of Chapter 1, we enumerated the virtues of biocatalyst enzyme and reviewed enzymatic polymerization in organic media. At the same time, chemical polymerizations (e.g., ATRP) appeared in chemoenzymatic synthesis reported previously were summarized in brief. Subsequently, we introduced in detail chemoenzymatic polymerization given in previous reports. More importantly, we sum up the strategies, synthesis method, functionality and potential application of chemoenzymatic synthesis related to ATRP. In the last section, we reviewed the"crew-cut"aggregates formed from amphiphilic diblock copolymers.In Chapter 2, we developed a novel bifunctional initiator bridged between eROP and ATRP. This initiator TCE contains a single primary alcohol group to initiate enzymatic ROP and an activated trichloromethyl group, an effective initiating group for ATRP. The -CCl3 terminated PCLmacroinitiator, resulted from TCE-initiated eROP of CL catalyzed by Novozyme 435, permits subsequent block-ATRP of St and GMA, The composition of the resulting diblock copolymer PCL-b-PSt and PCL-b-PGMA was confirmed by NMR,IR and GPC analysis. In addition, we also studied self-assembly of the diblock copolymer PCL-b-PSt and PCL-b-PGMA into polymeric nanospheres in aqueous media, nanoscale micelles have a spherical shape and a mean diameter.The above bifunctional initiator method permitted a sequential two-step synthesis combining enzyme and ATRP catalysis without an intermediate workup or modification steps, it simplified preparation procedure. However, the disadvantage of this strategy is ill-definition and simplex configuration of the product, i.e. only diblock structure. Thus, a novel strategy―End-group Modification method appeared in Chapter 3. Methanol/ethylene glycol initiated eROP of CL to synthesize the hydroxyl group terminated polyester PCL-OH/HO-PCL-OH. Theα-bromoester terminated macroinitiator PCL-Br/Br-PCL-Br were obtained in the subsequent modification of end hydroxyl groups and suitable for block-ATRP of St and GMA. Diblock copolymers PCL-b-PSt/PCL-b-PGMA and tribolck copolymers PSt-b-PCL-b-PSt/ PGMA-b-PCL-b-PGMA were successfully synthesized. NMR, GPC and IR analysis testified the copolymer structure as expected. The chapter chose epoxy-based diblock copolymer PCL-b-PGMA as an typical example and studied its self-assembly behavior in aqueous solution. The influence of the copolymer composition on the dimension of the resulting micelles was investigated in detail. The increasing PGMA content in copolymer resulted in increasing polymer chain aggregation number in copolymer micelle to make its diameter increase, at the same time, we also observed the formation of larger micelles aggregates.In Chapter 4, we carried out the chemoenzymatic synthesis of a novel amphiphilic CBABC-type pentablock copolymer PSt-b-PCL-b-PEO-b-PCL-b-PSt. The strategy was the same as that used in the preparation of tribolck copolymer PSt-b-PCL-b-PSt in Chapter 3, except that the initiator ethylene glycol was replaced with dihydroxyl PEO during eROP. The resulting pentablock copolymer can self-assemble into"crew-cut"aggregates. Surprisingly, the aggregates of various morphologies were observed, such as normal spheres, nonarods, lamella, vesicles, nanotubule, etc. To our knowledge, this is the first example of crew-cut aggregates of amphiphilic symmetric pentablock copolymers. The study showed the morphologies of"crew-cut"aggregates were affected by the block copolymer composition as well as the copolymer concentration in the initial THF solution. The higher PSt content in pentablock copolymer and the lower copolymer concentration in THF enabled the change of the aggregates for the more stable morphologies, from sphere to rod, to bilayers (i. e., vesicles, nanotubules and lamella). In conclusion, the copolymer composition played a major role in determining the morphologies of the aggregates; however, the copolymer concentration was also relevant.In Chapter 3 and Chapter 4, the strategy―End-group Modification method was used successfully in the synthesis of diblock copolymer, triblock copolymer and pentablock copolymer, which developed the categories of the material from chemoenzymatic techniques. In addition, the research on chemoenzymatic polymerization in Chapter 2⁴ was mostly involved in eROP; the successful synthesis of block copolymers indicated the good compatibility between eROP and ATRP. However, the combination of enzymatic polycondensation and ATRP was not yet reported in previous literature.In Chapter 5, our group proposed a simple strategy for a novel idea, i.e. enzymatic polycondensation was combined with ATRP to inspect further the compatibility between biocatalytic technique and chemocatalytic technique. A novelω-hydroxyester 2,2,2-trichloroethyl 10-hydroxydecanate P(TCE-10-HD) was firstly synthesized and used in eSCP to obtain linear polyester P(TCE-10-HD), whose terminal was occupied by the ATRP initiating groups, -CCl₃. The macroinitiator started the ATRP of St and GMA to prepare diblock copolymer P(TCE-10-HD)-b-PSt and P(TCE-10-HD)-b-PGMA. The introduce of eSCP expanded the category of enzymatic polymerization in chemoenzymatic polymerization, which inaugurated a new research domain.