Thiazoliums had been developed as a non-metal catalyst for bulk ring-opening polymerization (ROP) of cyclic esters

having the advantages of high stability

available for various monomers

and good controllability to polymerization. However

in order to achieve efficient catalysis under bulk polymerization conditions

fluorine-containing anions were generally used for preparing thiazoliums to promote the compatibility between catalysts and monomers

which was not conducive to the biosafety of the polymerization products. In this work

a built-in thiazolium chloride catalyst using mesoporous PS microsphere with high specific surface as the carrier was developed to achieve effective catalysis for ROP without introducing fluorine-containing anions. Through quaternization reaction between 4-methylthiazole and chloromethylated PS mesoporous microspheres (PS-CH

2

Cl)

built-in thiazolium chloride ([Thi

]

Cl@PS) catalyst supported by PS mesoporous microspheres was prepared. According to optical microscope

scanning electron microscope (SEM)

and BET measurement

the [Thi

]

Cl@PS (specific surface area 137 m

2

·g

-1

) with micron-size (50-250 μm

mean diameter 153 μm)

regular sphere morphology and a large number of inside pores (pore volume 0.31 cm

3

·g

-1

pore size 6.46 nm) were composed of compact accumulated nanoparticles. Based on FTIR and elemental analysis

the loading amount of thiazolium chloride in mesoporous PS microsphere was 0.67 mmol/g. Similar to the small molecular thiazolium catalysts

the [Thi

]

Cl@PS heterogeneous catalyst could selectively catalyze ROP of cyclic esters with relatively low steric hindrance (

i.e.

ε‍

-caprolactone

δ‍

-valerolactone

p

-dioxanone

and glycolide). Based on kinetic studies for catalyzing ROP of

ε

-caprolactone

both the [Thi

]

Cl@PS and small molecular thiazolium catalysts show "slow initiation" characteristics and first-ordered dynamics after fully initiation. The similar monomer selectivity and kinetic mode between the [Thi

]

Cl@PS heterogeneous catalyst and fluorine-containing small molecular thiazolium homogeneous catalyst suggest that they have a similar catalytic mechanism. Besides

the polymerization rate constants obtained from kinetic curves after fully initiation indicated that the [Thi

]

Cl@PS has medium catalytic efficiency (0.75 h

-1

·mol

-1

·L) relative to fluorine-containing small molecular thiazolium catalysts

i.e.

[Thi

]

PF

6

(7.50 h

-1

·mol

-1

·L)

[Thi

]

Tf

2

N (0.80 h

-1

·mol

-1

·L)

and [Thi

]

BF

4

(0.28 h

-1

·mol

-1

·L). Benefiting from the heterogeneous catalytic mode of [Thi

]

Cl@PS microspheres

it could be easily separated from the reaction system and recycled by dissolving the crude product in chloroform and filtration. Moreover

the recycled [Thi

]

Cl@PS was reused as catalyst for ROP

and showed similar catalyzing activity

compared to the original cycle. However

owing to the residual P

CL in microsphere

both molecular weight and polydispersity of yield PCL with recycled catalyst exhibited slight increase

suggesting that the controllability of polymerization also decreased.