This paper reports 'Catalyst-free decarboxylation of 4-hydroxycinnamic acids:
efficient synthesis of 4-vinylphenols'

At the outset, the title reaction has been already studied well and there exists adequate literature reports on catalyst free decarboxylation of cinnamic acids in general. In particular, the synthesis of 4-vinylphenol from 4-hydroxy cinnamic acid example is known under normal conditions. A few relevant papers (obtained from search engine) which deal with the same are given below.

Thus, the paper does not reveal a depth and not ready for a publication yet.

Having said the demerits, the following is suggested incase the authors want to consider.

The dimerization of 4-vinylphenol leading to dimers (2aa/2ff/2ll) under catalyst free condition may be of interest and will bring merit to the investigation if optimized, expanded, and studied in a comprehensive manner. Substrate scope elaboration and generality and application for the dimers would be interesting to explore. Unfortunately, only three examples have been shown. Thus after a meticulous major revision the paper may be re-submitted for consideration.
The paper in its current form not recommended given the literature precedence as said above.

For a few paper dealing with catalyst free decarboxylation of title compound, see:
in DMF 48 h, 28 oC
Efficient synthesis of hydroxystyrenes via biocatalytic decarboxylation/deacetylation of substituted cinnamic acids by newly isolated Pantoea agglomerans strains

By Sharma, Upendra K. et al
From Journal of the Science of Food and Agriculture, 92(3), 610-617; 2012

in water at rt 48 h
New greener alternatives for bioreduction of aromatic aldehydes and decarboxylation of aromatic acids using juice of fruits

By Misra, Kaushik et al
From Journal of Molecular Catalysis B: Enzymatic, 82, 92-95; 2012

• in water at 30 oC, ph 7.4
  4-Vinylphenol production from glucose using recombinant Streptomyces mobaraense expressing a tyrosine ammonia lyase from Rhodobacter sphaeroides

By Fujiwara, Ryosuke et al
From Biotechnology Letters, 38(9), 1543-1549; 2016